Gas discharge devices



Nov. 11, 1958 s. JEFFERSON GAS DISCHARGE DEVICES Filed July 2; 1954Attorney United States Patent 2,860,269 GAS DISCHARGE DEVICES SidneyJefferson, Abingdon, England, assignor, by mesne assignments, to theUnited States ofAmerie-a as repre sented by the United States AtomicEnergy Zomrnission Application July 2, 1954, Serial No. 441,080 Claims.(Cl. 313-54) This invention relates to gas discharge devices such ascold cathode tubes and is concerned with a method and means forintroducing tritium gas into the envelope of such a device for thepurpose of maintaining the discharge path in an ionised condition.

According to the invention tritium gas is initially introduced into agas discharge device in the form of a seed of metal wire strip or tubeimpregnated or containing said tritium gas and secured within theenvelope of the device in a position such that after the device has beende-gassed and sealed it can be discretely heated by, for example,eddy-current heating, to effect release of the tritium gas into theenvelope.

The tritium seed is preferably spot welded across the legs of a stirrupwhich is in turn welded to part of an electrode structure of the devicein the manner of a getter.

The tritium released into the envelope will probably be deposited on theelectrode structure and walls of the envelope. A means, in accordancewith a feature of the invention, for causing the tritium to be depositedover a selected region of the electrode structure or walls consists inproviding a deposit of tantalum or zirconium over said region. Suchmeans may comprise a short length of zirconium or tantalum wire spotwelded across the legs of a stirrup, welded to an electrode adjacentsaid region. By evaporating the wire by eddy-current heating afterdegassing of the discharge device, but before releasing the tritium, therequired deposit is obtained in the selected region. Alternatively, thezirconium or tantalum wire may be spot welded across two insulatedelectrodes and fused by passing a current therethrough.

Embodiments of the invention will now be described with reference to theaccompanying drawing wherein:

Fig. 1 is a side elevation partly in section of one form of tritiumseed.

Fig. 2 is a perspective view of another form of tritium seed securedacross the legs of a stirrup.

Fig. 3 is a view similar to Fig. 2 showing yet another form of seed andFig. 4 is a diagrammatic side elevation of a cold cathode diode tubeembodying alternative forms of the invention.

In Fig. 1 'the seed of the invention comprises a fine wire 1 of highlypurified zirconium impregnated with tritium gas and provided with acoating 2 of copper. Another form of seed is shown in Fig. 2 andcomprises a ribbon 3 of tungsten coated on one face with zirconiumimpregnated with tritium gas, folded in two along a longitudinal centreline with the coating inside, and sealed along the three open edges 4.The tungsten ribbon is about .002 in. thick and the dimensions whenfolded are about 3 mm. long by .5 mm. wide. The coating of zirconium isabout 2 microns thick and is deposited by the method of vacuumvaporisation.

impregnation of the coating (or of thewire of Fig. 1) with tritium isachieved by heating the coated ribbon in an atmosphere of tritium for2-3 minutes at about 400 C. before seam welding the edges 4.

2,860,269 Patented, Nov. 1 1., 1958 In Fig. 2 the seed is shown spotwelded at each end to the flattened endsS of the legs of a nickel wirestirrup 6. The spot welds are made through the end seam 4 to avoidpuncturing the ribbon 3.

Yet another form of seed in accordance withthe invention is shown inFig. 3 as comprising a nickel tube 7 filled with tritium gas. The tubehas an internal diameter of .008 in. and a wall thickness of .001 in.The length is.2 mm. and is such as to hold about micro curies of puretritium. Such a seed may be manufactured by filling a long length of thetubing with tritium gas and cutting it into 2 mm. lengths with a blunttool which flattens the ends 8 for a short distance. The seed 7 is shownattached to a nickel stirrup 6 similar to the stirrup 6 of Fig. 2.. Spotwelding of the ends 8 to the-flattened endsS .of the stirrup fi isconveniently done in one operation. Fig. 4 shows atypical cold cathodediode tube 9 embodying the invention. The electrode structure comprisesa thimble shaped anode 10 supported on wires 11 and a disc-like cathode12 supported on wires 13. The anodecathode space or discharge path whichit is desired to maintain in an ionised condition is indicated at 14.One method of embodying the invention in the tube 9 is to spot-weld astirrup 6 fitted with a seed 3 as shown (or a seed 1 or "1) to a wire 15welded to one of the electrode support wires such as one of the Wires 11such that the stirrup 6 is well clear of the electrode structure and ina plane at right angles to the plane of said structure.

After the tube has been de-gassed and sealed in the normal manner, theloop formed by the stirrup 6 and seed 3 is then eddy-current heated bymeans of a coil C located outside the envelope and supplied withalternating current. At red heat the tube 3 bursts or leaks sufficientlyto release the tritium into the envelope 9.

An alternative method of embodying a seed in the tube 9 is to provide anadditional lead 16 and to spot weld the seed 7 as shown (or a seed 1 or3) between said lead 16 and one of the main electrode supports 11. Theseed 7 may then be heated to red heat or fused by passing a currentthrough it. This method can be used when the seed is required to belocated in a position in which it cannot readily be heated byeddy-currents, such as within a hollow electrode structure.

The released tritium is found to be deposited on the electrode structureand the walls of the tube and it is desirable to locate the seed as nearas possible to the discharge gap 14. In order to encourage the tritiumto be deposited in the region of the discharge gap, even if the seed islocated some distance from the gap as shown in Fig. 4, a short length oftantalum or zirconium wire 17 is spot welded across two electrode leadssuch as the leads 11 and 13 and the wire is fused by passing a currenttherethrough prior to releasing the tritium. The result is a deposit oftantalum or zirconium 18 on the walls of the tube and on the electrodestructure in the immediate vicinity of the gap 14. When, thereafter, thetritium is released into the envelope it is selectively absorbed by thetantalum or zirconium in the region of the gap where it is mostlyrequired.

I claim:

1. A gas discharge device comprising an envelope, an electrode structurecomprising an anode and cathode with in said envelope, a plurality ofconductive supports, a metallic seed containing tritium gas connectedbetween a first pair 'of said supports and disposed apart from saidanode and cathode to form an independent electric circuit within saidtube, a filament selected from the group consisting of zirconium andtantalum disposed adjacent said electrode structure and connectedbetween a second pair of said supports to form a separate electriccircuit for vaporization of said filament prior to release of tritiumfrom said seed.

2. A gas discharge device as claimed in claim 1 wherein said seedcomprises a length of nickel tubing containing tritium gas and sealed ateach end.

3. A gas discharge device as claimed in claim 1 wherein said seedconstitutes a filament connected between said first pair of conductivesupports, electrical terminals outside the envelope, and an electricalconnection from each of said first pair of conductive supports to aseparate one of said terminals to provide an electrical circuit forheating said filament from an external current source.

4. A gas discharge device comprising an envelope, an electrode structurecomprising an anode and cathode within said envelope, a plurality ofconductive supports, a metallic seed containing tritium gas connectedbetween a first pair of said supports and disposed apart from said anodeand cathode to form an independent electric circuit, said seedcomprising a zirconium Wire impregnated with tritium and coated withcopper, and a filament selected from the group consisting of zirconiumand tantalum disposed adjacent said electrode structure and con-References Cited in the file of this patent UNITED STATES PATENTS2,354,786 Wall Aug. 1, 1944 2,576,100 Brown Nov. 27, 1951 2,617,956Hamvas Nov. 11, 1952 2,682,619 Landrey June 29, 1954 2,689,918 YoumansSept. 21, 1954

1. A GAS DISCHARGE DEVICE COMPRISING AN ENVELOPE, AN ELECTRODE STRUCTURECOMPRISING AN ANODE AND CATHODE WITHIN SAID ENVELOPE, A PLURALITY OFCONDUCTIVE SUPPORTS, A METALLIC SEED CONTAINING TRITIUM GAS CONNECTEDBETWEEN A FIRST PAIR OF SAID SUPPORTS AND DISPOSED APART FROM SAID ANODEAND CATHODE TO FORM AN INDEPENDENT ELECTRIC CIRCIUT WITHIN SAID TUBE, AFILAMENT SELECTED FROM THE GROUP CONSISTING OF ZIRCONIUM AND TANTALUMDISPOSED ADJACENT SAID ELECTRODE STRUCTURE AND CONNECTED BETWEEN ASECOND PAIR OF SAID SUPPORTS TO FORM A SEPARATE ELECTRIC CIRCUIT FORVAPORIZATION OF SAID FILAMENT PRIOR TO RELEASE OF TRITIUM FROM SAIDSEED.